Understand about opening heart in solemn procession (7)
I believe the answer is:
cortege
'solemn procession' is the definition.
(I've seen this before)
'understand about opening heart' is the wordplay.
'understand' becomes 'get' (getting is a kind of understanding).
'about' is a reversal indicator.
'opening' means one lot of letters goes inside another (some letters open a gap in others).
'heart' becomes 'core' ('core' can be a synonym of 'heart').
'get' reversed gives 'teg'.
'teg' placed within 'core' is 'CORTEGE'.
'in' is the link.
(Other definitions for cortege that I've seen before include "train" , "Processing figures" , "Entourage, retinue" , "Solemn funeral procession" .)